Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $217.75   8.476%   $236.2065   $236.21   $236.20   $236.20  
  Purchase #2 $119.71   8.295%   $129.6399   $129.64   $129.65   $129.60  
  Purchase #3 $77.27   7.127%   $82.777   $82.78   $82.80   $82.80  
  Purchase #4 $216.61   12.604%   $243.9115   $243.91   $243.90   $243.90  
  Purchase #5 $156.67   12.451%   $176.177   $176.18   $176.20   $176.20  
  Purchase #6 $158.89   11.788%   $177.62   $177.62   $177.60   $177.60  
  Purchase #7 $46.45   3.392%   $48.0256   $48.03   $48.05   $48.00  
  7 purchase totals = $993.35       $1,094.3575   $1,094.37   $1,094.40   $1,094.30